Affectionately known as Kero-chan, he is the Sun Guardian of the Clow Cards and appoints Sakura as the Cardcaptor who will recapture the released Clow Cards. In the English dub of Cardcaptors, he is known as Keroberos.

The eventual protagonist of Tsubasa: Reservoir Chronicle who was originally thought to be Syaoran's evil clone but turns out to be the original. Due to a temporal paradox, he was born the son of his and Sakura's clones, who had both been reincarnated in the xxxHOLiC Universe.

The 53 Clow card created by Clow Reed. The Nothing was created in order to balance the immense positive magic of the Clow Cards containing the negative magic equivalent in magnitude to the other fifty-two cards. Anything that comes into contact with it will cease to exist.